The invention relates to a liquid jetting apparatus such as an ink jet recording apparatus, a display manufacturing apparatus, an electrode forming apparatus, a biochip manufacturing apparatus or the like, which can control ejection of liquid droplets from nozzle orifices by controlling supply of drive pulses to pressure generating elements in accordance with a jetting amount, as well as to a method for driving such an apparatus.
Various kinds of the liquid jetting apparatus have hitherto been known. For example, there have been known an image forming apparatus which records information on recording paper by jetting ink droplets, an electrode forming apparatus which forms an electrode on a board by jetting liquid-state electrode material, a biochip manufacturing apparatus which manufactures a biochip by jetting biological specimen, and a micropipette for jetting a predetermined amount of sample into a vessel.
A liquid jetting apparatus capable of changing the amount of liquid to be ejected from nozzle orifices with a view toward pursuing both higher-speed jetting operation and higher jetting amount accuracy has hitherto been known.
For example, an ink jet recording apparatus which is one kind of the liquid jetting apparatus has, for example, a recording head which has nozzle orifices communicating with a pressure chamber, and pressure generating elements capable of causing a change in the pressure of the ink stored in the pressure chamber; and a drive signal generator capable of producing a drive signal to be supplied to the pressure generating elements. The drive signal is a single signal formed by connecting a plurality of drive pulses into a string of pulses within one recording cycle. A required portion of the drive signal is supplied to the pressure generating element in accordance with recording data (i.e., gradation data), thereby changing the amount of ink to be ejected from a nozzle orifice. Such a configuration is disclosed in Japanese Patent Publication No. 10-81012A (see Page 9 and FIG. 9).
However, a related-art configuration in which a required portion of a single drive signal is supplied to pressure generating elements encounters difficulty in causing a jetting head (recording head) to sufficiently offer original performance thereof. More specifically, since a plurality of drive pulses are included in one jetting (recording cycle), there is no alternative but to actuate a jetting head (i.e., a pressure generating element) at a frequency lower than the maximum frequency at which the jetting head can be actuated.
It is therefore an object of the invention to provide a liquid jetting apparatus which can be constructed so as to be able to actuate a jetting head at a higher frequency, along with a method for driving such an apparatus.
In order to achieve the above object, according to the invention, there is provided a liquid jetting apparatus, comprising:
a jetting head, provided with a nozzle orifice, a pressure chamber communicated with the nozzle orifice, and a piezoelectric element which is deformable to cause pressure fluctuation to liquid contained in the pressure chamber;
a drive signal generator, which simultaneously generates a plurality of drive signals, each provided with waveform elements including at least one drive pulse in every unit recording cycle, the drive pulse deforming the piezoelectric element to cause such pressure fluctuation as to eject a liquid droplet from the nozzle orifice;
a switcher, which selectively supplies at least one of the waveform elements included in one of the drive signals to the piezoelectric element; and
a switch controller, which controls a selective supply operation of the switcher in accordance with amount data which indicates an amount of the liquid droplet to be ejected,
wherein a time period in which the drive pulse is generated in one of the drive signal and that in another one of the drive signals overlap at least partly.
In such a configuration, the recording cycle can be shortened as compared with that achieved when a plurality of drive pulses are included in one drive signal in the form of a single pulse train. As a result, a jetting head can be actuated at a higher frequency.
Preferably, the waveform elements in each drive signal include a drive waveform element which constitutes the drive pulse, and a constant-potential waveform element which maintains a potential of the drive signal at a leading-end potential and a trailing-end potential thereof.
Here, the switch controller may control the switcher such that the drive waveform element in one of the drive signals and the drive waveform element in another one of the drive signals are supplied to the piezoelectric element in the unit jetting cycle.
Alternatively, the switch controller may control the switcher such that the drive waveform element in one of the drive signals and the constant-potential waveform element in another one of the drive signals are supplied to the piezoelectric element in the unit jetting cycle.
Alternatively, the switch controller controls the switcher such that the constant-potential waveform element in at least one of the drive signals is supplied to the piezoelectric element in the unit jetting cycle.
Since the waveform elements of respective drive signals are supplied in combination to the pressure generating element within a jetting cycle by switch controller, a jetting head can be actuated in a new pattern which is not originally contained in respective drive signals. As a result, complicated control can be realized while the drive frequency of the jetting head is enhanced.
When the constant-potential waveform element is used, the piezoelectric element can be maintained at a constant potential. As a result, there can be prevented a drop in the potential of the piezoelectric element, which would otherwise be caused by an electric discharge. Thus, there can be prevented occurrence of failures, such as erroneous ejection of a liquid droplet.
Preferably, the switcher includes a plurality of switches interposed between the drive signal generator and the piezoelectric element such that each of the switches is associated with one of the drive signals.
Here, it is preferable that the switch controller selectively activates one of the switches such that one of the drive signals associated with an activated switch is supplied to the piezoelectric element.
Preferably, the switcher includes a plurality of input contacts each associated with one of the drive signals and an output contact electrically connected to the piezoelectric element. Here, the switch controller selectively connects one of the input contacts and the output contact such that one of the drive signals associated with a selected input contact is supplied to the piezoelectric element. In this case, the switching control can be simplified.
Preferably, the drive signals include: a first drive signal, in which at least two first drive pulses each for ejecting a first amount of liquid droplet are arranged at a predetermined interval; and a second drive signal, in which at least one second drive pulse for ejecting a second amount of liquid droplet is generated at a timing between timings at which the first drive pulses are generated. Here, the predetermined interval is determined such that the first drive pulses are still arranged at the predetermined interval even when the first drive signal is successively selected in adjacent unit jetting cycles.
In such a configuration, there can be prevented occurrence of an offset, which would otherwise arise in an interval between ejection of liquid droplets, thereby enabling an improvement in jetting amount accuracy.
Here, it is preferable that the first drive pulse including: an expanding element, in which a potential of the first drive signal is varied from a reference potential to a first potential at a constant gradient, so that a volume of the pressure chamber is expanded from a reference volume to a first volume; and first holding element, which maintains the volume of the pressure chamber at the first volume. On the other hand, the second drive pulse including: a second holding element, in which a potential of the second drive signal is maintained at the first potential to maintain the volume of the pressure chamber at the first volume; and a contracting element, in which the potential of the second drive signal is varied from the first potential to the reference potential at a constant gradient, so that the volume of the pressure chamber is contracted from the first volume to the reference volume. Here, the switch controller controls the switcher so as to supply the expanding element, the first holding element, the second holding element and the contracting element, to cause pressure fluctuation such an extent that no liquid droplet is ejected, when the amount data indicates no jetting is to be performed.
Further, it is preferable that; each of the first drive pulses is interposed between first constant-potential waveform elements which maintain a potential of the first drive signal at a reference potential so that an initial end and a termination end of each first drive pulse are set to the reference potential; the second drive pulse is interposed between second constant-potential waveform elements which maintain a potential of the second drive signal at the reference potential so that an initial end and a termination end of the second drive pulse are set to the reference potential; and the switch controller controls the switcher so as to supply one of the first drive pulses and one of the second constant-potential waveform element, so that a potential of the piezoelectric vibrator is set to the reference potential while the first drive pulse is not supplied, when the amount data indicates the first amount of liquid droplet to be ejected.
According to the invention, there is also provided a method of driving a liquid jetting apparatus which comprises a jetting head, provided with a nozzle orifice, a pressure chamber communicated with the nozzle orifice, and a piezoelectric element which is deformable to cause pressure fluctuation to liquid contained in the pressure chamber, the method comprising the steps of:
generating simultaneously a plurality of drive signals, each provided with waveform elements including at least one drive pulse in every unit jetting cycle, the drive pulse deforming the piezoelectric element to cause such pressure fluctuation as to eject a liquid droplet from the nozzle orifice;
providing a switcher which selectively supplies at least one of the waveform elements included in one of the drive signals to the piezoelectric element; and
controlling a selective supply operation of the switcher in accordance with amount data which indicates an amount of the liquid droplet to be ejected,
wherein a time period in which the drive pulse is generated in one of the drive signal and that in another one of the drive signals overlap at least partly.